Fix Fatal error: Access to undeclared static property: Theme::$parent_th...

...eme in /oc/common/classes/oc/view.php:77

Fix Fatal error: Access to undeclared static property: Theme::$parent_theme in /oc/common/classes/oc/view.php on line 77
This only happens if you have an old version of OC installed, since in the class theme the $parent_theme variable exists. Weird you get that error: https://github.com/open-classifieds/common/blob/master/classes/oc/theme.php#L16